A mail insertion system or a “mailpiece inserter” is commonly employed for producing mailpieces intended for use in the mailstream. Such mailpiece inserters are typically used by organizations such as banks, insurance companies and utility companies for producing a large volume of specific mail communications where the contents of each mailpiece are directed to a particular addressee. Also, other organizations, such as direct mailers, use mailpiece inserters for producing mass mailings where the contents of each mailpiece are substantially identical with respect to each addressee.
In many respects, a typical inserter system resembles a manufacturing assembly line. Sheets and other raw materials (i.e., a web of paper stock, enclosures, and envelopes) enter the inserter system as inputs. Various modules or workstations in the inserter system work cooperatively to process the sheets until a finished mail piece is produced. Typically, inserter systems prepare mail pieces by arranging preprinted sheets of material into a collation, i.e., the content material of the mail piece, on a transport deck. The collation of preprinted sheets may continue to a chassis module where additional sheets or inserts may be added based upon predefined criteria, e.g., an insert being sent to addressees in a particular geographic region. Subsequently, the collation may be folded and placed into envelopes. Once filled, the envelopes are closed, sealed, weighed, and sorted. A postage meter may then be used to apply postage indicia based upon the weight and/or size of the mail piece.
One module, to which the present invention is directed, relates to the input section of an inserter wherein mailpiece sheet material is stacked in a shingled arrangement and singulated for creation of a mailpiece. In this module, the sheets are individually handled for collation, folding, insertion or other handling operation within the mailpiece insertion system to produce the mailpiece. Typically, the sheets are spread/laid over a horizontal transport deck and slowly conveyed to a rotating vacuum drum or cylinder which is disposed along the lower surface or underside of the sheet material. Furthermore, the leading edge of the stacked sheet material abuts and rests against a stationary stripper which is disposed above and slightly aft of the drum (i.e., its rotational axis).
The rotating vacuum drum/cylinder incorporates a plurality of apertures in fluid communication with a vacuum source for drawing air and developing a pressure differential along the underside of each sheet. As a sheet is conveyed along the deck, the leading edge thereof, disposed parallel to the axis of the vacuum cylinder, is brought into contact with the outer surface of the vacuum cylinder. The pressure differential produced by the vacuum source draws the sheet into frictional engagement with the cylinder and separates/singulates individual sheets from the stack by the rotating motion of the vacuum cylinder. That is, an individual sheet is separated from the stack by the vacuum drum/cylinder and is singulated, relative to the stacked sheets above, as the sheet follows a tangential path relative to the rotating circular drum.
Singulation may be augmented by a blower which introduces pressurized air between the sheets to separate the sheets as they frictionally engage the rotating drum/cylinder. That is, an air plenum may be disposed along each side of the stacked sheets to pump air between the sheets and reduce any fiber adhesion or interlock which may develop between the sheet material.
The rate of mailpiece fabrication is essentially limited by or to the speed of an inserter's least productive module (i.e., in terms of mailpiece throughput). Consequently, it is generally desirable to mitigate or eliminate sheet transport or transfer limitations wherever possible. While the various systems/mechanical apparatus discussed above greatly increase the rate of singulation, the transfer rate can be limited by the frictional interface developed between the stacked sheets of material. Such limitations, it will be appreciated, can adversely affect the rate or throughput of mailpiece fabrication.
A need, therefore, exists for a high throughput sheet feeder which mitigates or minimizes friction or adhesion between sheet material during singulation.